Airbus scored a landmark $9.75 billion order from Japan Airlines Co., breaking into territory long held exclusively by Boeing Co.

JAL ordered 31 A350 jetliners carrying a catalog price of ¥950 billion, with an option to buy 25 more of the long-distance planes, the companies said Monday. Deliveries will start in 2019 and roll out over six years.

The win for Airbus was the clearest example of the long-term effect on Boeing's...